The work proposed is the investigation of the purine nucleotide synthesis and degradation in human term placentas and guinea pig placentas. The focus is on the propertis, regulation and subcellular disposition in the human term placenta of enzymes producing and salvagins adenosine, e.g., 5'-nucleotidase, 5'-adenylate kinase and adenosine kinase, particularly as adenosine has been isolated from human term placentas after labor, and may have a role in the local regulation of blood flow in the placenta. To examine a possible correlation between between adenine nucleotide levels and duration of labor in human term placentas measurement of purine nuclesodies and adenine nucleotides in human term placentas will be made using high pressure liquid chromatography. The presence of pathways of de novo purine nucleotide biosynthesis in human and guinea pig placentas will be investigated using cell-free extracts and in vitro tissue preparations; the relative importance of de novo and salvage synthesis in normoxic and postanoxic conditions will be assessed. The data obtained as a result of these studies will contribute to the understanding of the placenta as an active metabolic organ.